Lithium ion battery cell balancing system and method, and a battery charging device with lithium ion battery cell balancing

ABSTRACT

Provided is a lithium ion rechargeable battery charging system with lithium cell balancing, including a lithium ion rechargeable battery and a battery charging device configured for charging the lithium ion rechargeable battery and wherein cell balancing of the lithium ion rechargeable battery cells of the lithium ion rechargeable battery continues for a predetermine period of time once a cell balancing mode begins.

FIELD

The present invention is directed to a lithium ion battery cellbalancing system and method, and a battery charging device comprising alithium ion battery cell balancing system and/or incorporating thelithium ion battery cell balancing method according to the presentinvention.

BACKGROUND

Currently, there exists a battery charger for charging a depleted ordischarged lithium ion rechargeable battery (e.g. depleted or dischargedlithium ion rechargeable vehicle battery). The existing battery chargeroperates in a manner that if the lithium ion rechargeable batteryvoltage of the battery charger reaches a cut-off voltage for a Lithiummode (e.g. 14.6V) while the battery charger is delivering current to thedepleted or discharged lithium ion rechargeable battery being charged,even during a soft start, the charge current is cut-off and a fuel gaugeon the display of the battery charger displays a solid green light (e.g.via a green LED in the fuel gauge), after an appropriate fuel gauge timeincrement.

Further, the existing battery charger will oscillate between a lithiummode and a stand-by mode during charging operation of the depleted ordischarged lithium ion rechargeable battery. Specifically, when charginga lithium ion rechargeable battery with a Battery Management System(BMS) and the lithium ion rechargeable battery cells are unbalanced, thebattery charger will oscillate between the lithium mode and thestand-by.

This is caused because the lithium ion rechargeable battery's BatteryManagement System (BMS) monitors each cell voltage. If a lithium ionrechargeable battery cell gets charged too high, the Battery ManagementSystem (BMS) will open the Charge FET to prevent further charging of theparticular lithium ion rechargeable battery cell. Meanwhile, an internalresistor in the Battery Management System (BMS) is connected to slowlydischarge the lithium ion rechargeable battery cell. The Charge FET willagain be closed once the over-voltage lithium ion rechargeable batterycell has discharged to a lower level.

When the Charge FET opens up, a diode is still present which allows adischarge path to the lithium ion rechargeable battery cells. This meansthat when the battery charger is connected to the lithium ionrechargeable battery, an internal voltage divider resistor network inthe battery charger will still sense a voltage at the terminals, and tryto drive a charge current. Since the Charge FET in the battery is open,no current is sensed by the charger, and the charger then goes back toStand-by mode.

Since the battery charger detects the battery voltage, it pols thebattery voltage every few seconds to see if a current can be applied.When trying to apply the current, the battery charger goes from Stand-bymode to Lithium mode. The battery charger will oscillate betweenstand-by mode and Lithium mode until the battery BMS closes the ChargeFET.

SUMMARY

The present invention is directed to a lithium ion battery cellbalancing system and/or method for charging a depleted or dischargedlithium ion rechargeable battery, and a battery charger comprising thelithium battery cell balancing system and/or incorporating the lithiumion battery cell balancing method according to the present invention.

The lithium ion battery cell balancing method comprises or consists of anumber of steps for balancing the multiple lithium ion rechargeablebattery cells of the lithium ion rechargeable battery, depending on theparticular type of battery charger (e.g. Constant Current (CC) typebattery charger or Constant Voltage (CV) type battery charger).

The presently described subject matter is also directed to a lithium ionrechargeable battery charging system and/or method for use in a batterycharger configured to charge a lithium ion rechargeable battery that hasa built in Battery Management System (BMS).

The lithium ion rechargeable battery comprises multiple lithium ionrechargeable battery cells connected together in an electrical seriesarrangement. The lithium ion rechargeable battery cells can becomeimbalanced relative to each other due to variations in capacities orloads on the various lithium ion rechargeable battery cells.Specifically, during charging operation the voltages of the lithium ionrechargeable battery cells become different relative to each other.

To keep the lithium ion rechargeable battery cells operating in a safevoltage range, the lithium ion rechargeable battery can include aBattery Management System (BMS). The role of the Battery ManagementSystem (BMS) is to monitor the voltages of the lithium ion rechargeablebattery cells and open up a Discharge FET, if any of the lithium ionrechargeable battery cells of the lithium ion rechargeable batterybecomes undercharged, and to open up a Charge FET, if any of the lithiumion rechargeable battery cells becomes overcharged.

The Battery Management System (BMS) can include a lithium ionrechargeable battery cell balance feature according to the presentinvention. The Battery Management System (BMS) can monitor eachindividual lithium ion rechargeable battery cell voltage inside of thelithium ion rechargeable battery. If a particular lithium ion batterycell becomes overcharged, the Battery Management System (BMS) will placea small resistive load across the particular lithium ion rechargeablebattery cell to slowly bleed charge off this particular lithium ionrechargeable battery cell. The resistive load on the particular lithiumion rechargeable battery cell is disconnected once the particularlithium ion rechargeable battery cell voltage decreases to a safethreshold.

During cell balancing of a lithium ion rechargeable battery withunbalanced lithium ion battery cells, the Battery Management System(BMS) can open/close the Charge FET numerous times as the internallithium ion rechargeable battery cells are slowly brought into balanceby the Battery Management System (BMS).

For charging a lithium ion rechargeable battery, a final step is to stayin a constant voltage (CV) mode and maintain a Taper Charge ThresholdVoltage at the battery charger terminals to allow time for the lithiumion rechargeable battery's internal Battery Management System (BMS) tocell balance. This time is called a Lithium Cell Balance Time, and canbe set, for example to 4 hours. However, this time can be programmable,and, for example, and can be adjusted to a different time duration (e.g.6 hours, 8 hours).

During the Lithium Cell Balance Time, the battery charger is in aconstant voltage (CV) mode. During this time, the battery charger needsto be able to distinguish between the lithium ion rechargeable battery'sBMS opening the Charge FET verses a user disconnecting a charger cablefrom the depleted or discharged lithium ion rechargeable battery beingcharged. If the Charge FET is opened up by the BMS, then the chargermust stay in the Lithium Cell Balance mode for the balance of theLithium Cell Balance Time. If the user disconnects the battery chargerfrom the lithium ion rechargeable battery, the battery charger must goto a Standby mode.

While the lithium ion rechargeable battery is in the Lithium CellBalance (LCB) mode, the battery charger output current is monitored. Ifthe charge current drops below the minimum detectable current level,then the charger starts checking the battery voltage every second.

To check the lithium ion rechargeable battery voltage, the batterycharger internally opens a circuit from the battery charger's constantvoltage supply to the lithium ion rechargeable battery, and thenmeasures the lithium ion rechargeable battery voltage. If the lithiumion rechargeable battery voltage has dropped below 10.5V, then the userdisconnects the battery charger cables from the lithium ion rechargeablebattery, and the battery charger goes to Standby mode. If the lithiumion rechargeable battery voltage is above 10.5V, then the BatteryManagement System (BMS) Charge FET opens up and the battery chargerreconnects the battery charger's constant voltage source to the lithiumion rechargeable battery until the next one (1) second lithium ionrechargeable battery voltage check time interval. If the lithium ionrechargeable battery starts pulling detectable current again, theinternal switch remains closed.

It is noted that the battery charger can still measure the lithium ionrechargeable battery voltage (minus a diode drop) when the Charge FET isopen because the freewheeling diode provides a current path for themeasurement.

There are two (2) modes of Lithium Cell Balancing (LCB). In the firstLithium Cell Balancing (1st LCB) mode when the lithium ion rechargeablebattery cells are not far out of balance, the Battery Management System(BMS) will not open up the charge FET during the first Lithium CellBalancing (1st LCB) mode. In this mode, a constant current (CC) typebattery charger just emulates a constant voltage (CV) type batterycharger. This is done by using a first soft start current level tocharge the lithium ion rechargeable battery until it hits 14.6V. Once ithits 14.6V, it turns off the current and waits for the voltage to dropto 14.4V. Once it hits 14.4V (along with some delay(s)), then it turnsthe first soft start current back on and repeats. So, basically theconstant current (CC) type battery charger emulates the constant voltage(CV) type battery charger by keeping the battery voltage in a tightvoltage range of 14.4V to 14.6V.

In the second Lithium Cell Balance (2nd LCB) mode, the lithium ionrechargeable battery cells are out of balance far enough for the BatteryManagement System (BMS) to open up the charge FET. The battery chargerhas to detect that the charge FET has opened up verses the userdisconnecting the terminals. Since the open charge FET still has a bodydiode connection, the battery charger can still measure the batteryvoltage, minus a diode drop. Therefore if the Battery Management System(BMS) opens up the charge FET, but the battery charger can still measurea battery voltage greater than (>) 10.5 volts, it can tell the lithiumion rechargeable battery is still connected. So, next the batterycharger has to be able to determine when the charge FET closes again. Itdoes this by polling the lithium ion rechargeable battery impedanceevery minute. During the polling, the battery charger attempts to forcea charge current. If no current is accepted, it knows that the chargeFET is still open. Once the charge FET closes, and on the next chargerpolling attempt, the battery charger will see that the lithium ionrechargeable battery is now accepting current, and will continuecharging at the first soft start level until the battery reaches 14.6Vor until the Battery Management System (BMS) opens up the charge FET. If14.6V is reached, it goes into the first Lithium Cell Balancing (1stLCB) mode. If the BMS opens up, it repeats the second Lithium CellBalancing (2nd LCB) mode.

The above is done either by the first Lithium Cell Balancing (1st LCB)mode, the second Lithium Cell Balancing (2nd LCB) mode, or combinedsecond Lithium Cell Balancing (2nd LCB) mode then first Lithium CellBalancing (1st LCB) mode for a set time of the Lithium Cell Balancing(LCB) operation.

For the battery charger, for example, 4 hours is selected, but this timeis arbitrary. The total time needed for a Battery Management System(BMS) to reach full cell balance is determined by how far the internallithium ion rechargeable battery cells are out of balance, and what sizeof balance load is used by the Battery Management System (BMS). Both ofthese factors are not observable by the battery charger.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagrammatic view of a lithium ion rechargeable battery witha Battery Management System (BMS).

FIG. 2 is a top planar view of the Battery Management System (BMS)showing the BMS connections of the lithium ion rechargeable battery.

FIG. 3 is perspective view of the Battery Management System (BMS) andlithium ion rechargeable battery showing the BMS connection with thelithium ion rechargeable battery.

FIG. 4 is a graph showing G2 7 AH (amp hour) Battery with 0.33 AHdischarged from Cell 1 (7 AH with 0.33 AH Discharged from Cell 1).

FIG. 5 is a graph showing G2 7 AH (amp hour) Battery with 0.33 AM addedto Cell #1 (Took multiple Charge Cycles) (7 AH Plus 0.33 AH AdditionalCharge added to C1).

FIG. 6 is a graph showing Previous Chart—Zoomed in to 40-45 Hr Timeframe(7 AH Plus 0.33 AH Additional Charge added to C1).

FIG. 7 is a graph showing G2 Cold Start Battery Charge Profile(Potential Typical Use Case) (7 AH Cold Start Battery after sitting onshelf a few months).

FIG. 8 is a graph showing G2 Short Discharge to Charge to MaintenanceCharge (Balanced Battery Slightly Discharged Then charged+100 HrMaintenance).

FIG. 9 is a graph showing Zoom in Timeframe of Previous Charge Log(Balanced Battery Slightly Discharged Then charged+100 Hr Maintenance).

FIG. 10 is a graph showing G10 7 AH fully charged with 0.45 AH removedfrom Cell 1 (G10 Firmv K 7 AH with 0.45 AH discharged from cell 1).

FIG. 11 is a graph showing Competitor Lithium Battery Charge Profile(Genius 2 Firmware Rev R Charging BTLI12A270CW Lithium Battery).

FIG. 12 is a graph showing Competitor Lithium Battery Charge Profile(Genius 5 Firmware Rev R Charging ATZ-10).

FIG. 13 is a graph showing Competitor Lithium Battery Charge Profile(Continuation of ATZ-10 Charge. Charge until BMS No Longer Opens; ThenDischarged and then Recharged. Note BMS Doesn't open on Recharge—BatteryCells remained balanced).

FIG. 14 is a graph showing Competitor Lithium Battery Charge Profile(Genius 5 Firmware Rev R charging battery ETX12A).

FIG. 15 is a graph showing NOCO Lithium Battery Charge Profile (Genius 2Firmware Rev R Charging NOCO NLP9).

FIG. 16 is a graph showing NOCO Lithium Battery Charge Profile (Genius 5Firmware Rev R Charging NOCO NLP14).

FIG. 17 is a graph showing NOCO Lithium Battery Charge Profile Genius 2Firmware Ver. S (Genius 2 Firmware Version 5 charging 7 AH Lithium withLCB-Cell 3 Imbalance).

FIG. 18 is a graph showing NOCO Lithium Battery Charge Profile Genius 10Firmware P (G 10 LCB Firmware Rev P 7 AH 12V Lithium @ 25C Cell 1 OverCharged).

DETAILED DESCRIPTION

A battery charging device 10 comprising a positive battery cable 14 anda negative battery cable 16 are connected to the lithium ionrechargeable battery 20, as shown in FIG. 1 . For example, the positivebattery cable 12 can be connected to the positive battery terminal 22 ofthe lithium ion rechargeable battery 20 (e.g. using a positive batteryclamp, not shown) and the negative battery cable 14 can be connected tothe negative battery terminal 24 of the lithium ion rechargeable battery20 (e.g. using a negative battery clamp, not shown).

The lithium ion rechargeable battery 20 comprises four (4) lithium ionrechargeable battery cells 26A, 26B, 26C, 26D connected together inelectrical series, a Battery Management System (BMS) 28 connected to thefour (4) lithium ion rechargeable battery cells 26A, 26B, 26C, 26D, aDischarge FET 30, and a Charge FET 32. The Discharge FET 30 and ChargeFET 32 are connected in electrical series with the four (4) lithium ionrechargeable battery cells 26A, 26B, 26C, 26D, as shown in FIG. 1 .

The Battery Management System (BMS) 28 comprises a printed circuit board34, as shown in FIG. 2 . The printed circuit board 34 comprises apositive external battery terminal/internal lithium ion rechargeablebattery positive battery connection 34A, a negative external batteryterminal 34B, and an internal lithium ion negative battery connection34C.

The Battery Management System (BMS) 28 is connected to the lithium ionrechargeable battery 20, as shown in FIG. 3 .

The battery charger 10 is configured and/or programed to charge thelithium ion rechargeable battery 20 in a particular manner. For example,the battery charger 10 is provided with a lithium ion rechargeablebattery cell balancing mode or feature (i.e. Lithium Cell Balance).

For example, the battery charge 10 operates as follows. If the lithiumion rechargeable battery voltage reaches the cut-off voltage for Lithiummode (e.g. 14.6V) while the battery charger is delivering current to thedepleted or discharged lithium ion rechargeable battery, even in a softstart mode, the battery charger will enter the Lithium Cell Balance(LCB) mode, for example, four (4) hours. The Lithium Cell Balance (LCB)mode is indicated by turning off the 25%, 50%, 75% fuel gauge LEDs onthe display of the battery charger while lighting the 100% LED (i.e.same as specific gravity optimization).

While in the Lithium Cell Balance (LCB) mode, the battery charger willturn off the charge current once the battery voltage reaches the cut-offvoltage. The charger will continue to monitor the battery voltage andonce it drops to 14.4V, the charger will resume charging at the lowestsoft start current (e.g. one-half (½) of the lowest soft start current,if the temperature is below 0° C.). The battery charger will turn offand on while the battery voltage is increasing to 14.6V and thendropping to 14.4V multiple times. The battery charger will cut-off for apredetermined time interval (e.g. one (1) minute) after reaching 14.6Vbefore the battery charger is allowed to turn on again, even if thebattery voltage has dropped past 14.4V.

After a predetermined time interval (e.g. four (4) hours) in the LithiumCell Balance mode, the battery charger will stop charging and indicate100% on the fuel gauge on the display of the battery charger.

Lithium Cell Balance Mode with BMS Oscillations

While charging the lithium ion rechargeable battery (Lithium mode), ifthe Battery Management System (BMS) of the lithium ion rechargeablebattery opens before the battery voltage reaches 14.6V as indicated byif the battery charger measures a voltage above the start voltage andbelow 14.6V, but cannot provide a charge current, the battery chargergoes into Lithium Cell Balance mode and starts a four (4) hour timer.The fuel gauge then sequences to a breathing green 100% LED.

The battery charger shall keep polling the voltage of the lithium ionrechargeable battery, but instead of going to stand-by mode in-betweenpolling attempts, the battery charger shall stay in Lithium Cell Balance(LCB) mode and the fuel gauge indicates a green 100% LED (e.g. abreathing green colored operating LED repeatedly glowing brighter anddimmer).

Once the battery charger hits this current balance mode, the BatteryManagement System (BMS) will be opening and closing randomly. Thebattery charger will continue to poll the voltage of the lithium ionrechargeable battery when the Battery Management System (BMS) closes theFET, once the FET is closed the battery charger will charge at thelowest soft start current (e.g. one-half (½) of lowest soft startcurrent if below 0° C.).

If the lithium ion rechargeable battery's internal lithium ion batterycells equalize to the point where the Battery Management System (BMS) nolonger opens and the battery voltage rises to 14.6 volts, the chargershall operate as described above, except the four (4) hour timer shallnot be reset.

After the four (4) hours in the cell balance mode, the battery chargerstops charging and indicates 100% on the fuel gauge on the display ofthe battery charger. If the battery charger ever detects that thebattery voltage goes below the start voltage, the battery charger goesto stand-by mode.

1. A lithium ion rechargeable battery charging system with lithium cellbalancing, the system comprising: a lithium ion rechargeable batterycomprising multiple lithium ion rechargeable battery cells connectedtogether in electrical series and a battery management system (BMS), thebattery management system (BMS) comprises a discharged field-effecttransistor (FET) and a charge field-effect transistor (FET); and abattery charging device configured for charging the lithium ionrechargeable battery, the battery charging device connected orconnectable to the lithium ion rechargeable battery during charging ofthe lithium ion rechargeable battery, the battery charging deviceconfigured for charging the lithium ion rechargeable battery, whereinthe battery management system (BMS) is configured to monitor voltages ofthe multiple lithium ion rechargeable battery cells of the lithium ionrechargeable battery and open up the discharge field-effect transistor(FET), if any of the multiple lithium ion rechargeable battery cellsbecomes undercharged and to open up the charge field-effect transistor(FET), if any of the lithium ion rechargeable battery cells becomesovercharged when charging the lithium ion rechargeable battery with thebattery charging device, wherein the battery management system (BMS) isconfigured to monitor the voltage of each lithium ion rechargeablebattery cell of the lithium ion rechargeable battery and, if one lithiumion rechargeable battery cell becomes overcharged, the batterymanagement system (BMS) will place a resistive load across thisparticular lithium ion battery cell to slowly bleed charge off thisparticular lithium ion rechargeable battery cell, and then the batterymanagement system (BMS) disconnects the resistive load once voltage ofthis particular lithium ion rechargeable battery cell decreases to asafe threshold when charging the lithium ion rechargeable battery withthe battery charging device, and wherein cell balancing of the lithiumion rechargeable battery cells of the lithium ion rechargeable batterycontinues for a predetermine period of time once a cell balancing modebegins.
 2. The system according to claim 1, wherein the batterymanagement system (BMS) is configured to open and close multiple timesas the lithium ion rechargeable battery cells are brought into balanceby the battery management system (BMS) when charging the lithium ionrechargeable battery with the battery charging device.
 3. The systemaccording to claim 1, wherein the charging the lithium ion rechargeablebattery is in a constant voltage mode while maintaining a taper chargethreshold voltage at terminals of the battery charging device to allowtime for the battery management system (BMS) to balance the lithium ionrechargeable battery cells.
 4. The system according to claim 3, whereinthe time is a lithium ion cell balance time.
 5. The system according toclaim 4, wherein the lithium ion cell balance time is set for a fixedlength of time.
 6. The system according to claim 5, wherein the lithiumion cell balance time is preset at four (4) hours.
 7. The systemaccording to claim 5, wherein while in the lithium ion cell balancetime, monitor the battery charge output current and, if a charge currentfrom the battery charging device to the lithium ion rechargeable batterydrops below a minimum detectable current level, then the batterycharging device checks the lithium ion rechargeable battery voltagerepeatedly after a predetermined period of time.
 8. The system accordingto claim 7, wherein the battery charging device checks the lithium ionrechargeable battery voltage every second.
 9. The system according toclaim 7, wherein the battery charging device internally opens a circuitfrom the battery charging device's constant voltage supply to thelithium ion rechargeable battery and then the battery voltage of thelithium ion rechargeable battery is measured.
 10. The system accordingto claim 9, wherein if the battery voltage of the lithium ionrechargeable battery drops below 10.5 V, then the user disconnects thebattery charging device from the lithium ion rechargeable battery andthe battery charging goes to standby mode.
 11. The system according toclaim 8, wherein if the lithium ion rechargeable battery is above 10.5 Vthen the battery management system (BMS) charge FET opens up and thebattery charging device reconnects the battery charging device'sconstant voltage source to the lithium ion rechargeable battery until anext one (1) second lithium ion rechargeable battery voltage checkinterval, and wherein if the lithium ion rechargeable battery startspulling detectable current again, then an internal switch remainsclosed.
 12. The system according to claim 11, wherein the batterycharging device can still measure the lithium ion rechargeable batteryvoltage minus a diode drop when the charge FET is open because afreewheeling diode provides a current path for the measurement.
 13. Thesystem according to claim 1, wherein, if the lithium ion rechargeablebattery cells are not far out of balance, the battery management system(BMS) will not open up the charge FET during lithium cell balancing,wherein a first soft start current level is used to charge the depletedor discharged battery until the depleted or discharged battery hits 14.6V, wherein once the depleted or discharged battery hits 14.6 V thebattery management system (BMS) turns off current and waits for thevoltage of the lithium ion rechargeable battery to drop to 14.4 V, andwherein once the lithium ion rechargeable battery hits 14.4 V then thebattery management system (BMS) turns the first soft start current levelback on and repeats.
 14. The system according to claim 1, wherein whenthe lithium ion rechargeable battery cells are out of balance far enoughfor the battery management system (BMS) to open up the charge FET, andwherein the battery charging device polls the lithium ion rechargeablebattery impedance every minute to determine when the charge FET closesagain and the battery charging device begins charging the lithium ionrechargeable battery at the first soft start charging level until thelithium ion rechargeable battery reaches 14.6 V or until the batterymanagement system (BMS) opens up the charge FET.
 15. A lithium cellbalancing method for use in charging a lithium ion rechargeable batterycomprising multiple lithium ion battery cells and a battery managementsystem (BMS) comprising a charge FET and discharge FET using a batterycharging device, the lithium cell balancing method, comprising:monitoring the voltages of the lithium ion rechargeable battery cellsand opening up the discharge FET, if any of the lithium ion rechargeablebattery cells of the lithium ion rechargeable battery becomesundercharged, and opening up the charge FET, if any of the lithium ionrechargeable battery cells of the lithium ion rechargeable batterybecomes overcharged. placing a small resistive load across a particularlithium ion rechargeable battery cell to slowly bleed charge off thisparticular lithium ion rechargeable battery cell; disconnecting thesmall resistive load across the particular lithium ion rechargeablebattery once the particular lithium ion rechargeable battery cellvoltage decreases to a safe threshold′ opening and closing the chargeFET of the battery management system (BMS) multiple times as theinternal lithium ion rechargeable battery cells are brought into balanceby the battery management system (BMS); and staying in a constantvoltage (CV) mode and maintaining a taper charge threshold voltage atterminals of the battery charging device to allow time for the batterymanagement system (BMS) of the lithium ion rechargeable battery tolithium cell balance the lithium ion rechargeable battery cells of thelithium ion rechargeable battery during a lithium cell balance time fora predetermine period of time.
 16. The method according to claim 15,wherein the lithium cell balance time is a fixed period of time.
 17. Themethod according to claim 15, wherein the lithium cell balance time is avariable period of time.
 18. The method according to claim 15, whereinthe lithium cell balance time is a programmable and can be adjusted todifferent time durations.
 19. The method according to claim 15, furthercomprising distinguishing between the battery management system (BMS)opening the charge FET verses a user disconnecting a charger cable fromthe lithium ion rechargeable battery being charged.
 20. The methodaccording to claim 19, wherein, if the charge FET is opened up by thebattery management system (BMS), the battery charging device must stayin the lithium cell balance mode for a balance of the lithium cellbalance time, and if the user disconnects the battery charging devicefrom the lithium ion rechargeable battery, the battery charging devicemust go to a standby mode.
 21. The method according to claim 15, furthercomprising monitoring the battery charging device output current whilethe lithium ion rechargeable battery is in the lithium cell balance(LCB) mode, and if the charge current drops below the minimum detectablecurrent level, then the battery charging device starts repeatedlychecking the lithium ion rechargeable battery voltage.
 22. The methodaccording to claim 21, wherein the battery charging device startsrepeatedly checking the lithium ion rechargeable battery device voltageevery second.
 23. The method according to claim 22, wherein to check thelithium ion rechargeable battery voltage, the battery charging deviceinternally opens a circuit from the battery charging device's constantvoltage supply to the lithium ion rechargeable battery, and thenmeasures the lithium ion rechargeable battery voltage, and if thelithium ion rechargeable battery voltage has dropped below 10.5V, thenthe user disconnects battery charger cables from the lithium ionrechargeable battery, and the battery charger goes to standby mode; andif the lithium ion rechargeable battery voltage is above 10.5V, then thebattery management system (BMS) charge FET opens up and the batterycharging device reconnects the battery charging device's constantvoltage source to the lithium ion rechargeable battery until a next one(1) second lithium ion rechargeable battery voltage check time interval,and if the lithium ion rechargeable battery starts pulling detectablecurrent again, an internal switch remains closed.
 24. The methodaccording to claim 23, wherein the battery charging device can stillmeasure the lithium ion rechargeable battery voltage minus a diode dropwhen the charge FET is open because a freewheeling diode provides acurrent path for voltage measurement.
 25. The method according to claim15, wherein the lithium cell balancing method comprises multiple modesof lithium cell balancing.
 26. The method according to claim 25, whereinthe lithium cell balancing method comprises a first lithium cellbalancing mode when the lithium ion rechargeable battery cells are notfar out of balance and the battery management system (BMS) and a secondlithium cell balance mode when the lithium ion rechargeable batterycells are out of balance far enough for the battery management system(BMS) to open up the charge FET.
 27. The method according to claim 26,wherein the battery management system (BMS) does not open up the chargeFET during the first lithium cell balancing mode.
 28. The methodaccording to claim 27, wherein a constant current (CC) type batterycharging device just emulates a constant voltage (CV) type batterycharging device during the first lithium cell balancing mode.
 29. Themethod according to claim 28, wherein a first soft start current levelis used to charge the lithium ion rechargeable battery until it hits14.6V, and once it hits 14.6V, it turns off the current and waits forthe voltage to drop to 14.4V, and once it hits 14.4V along with at leastone time delay, then it turns the first soft start current back on andrepeats so that the constant current (CC) type battery charging deviceemulates the constant voltage (CV) type battery charging device bykeeping the battery voltage in a tight voltage range of 14.4V to 14.6V.30. The method according to claim 26, wherein in the second lithium cellbalance mode, the battery charging device detects that the charge FEThas opened up verses the user disconnecting the terminals, and since theopen charge FET still has a body diode connection, the battery chargingdevice can still measure the battery voltage, minus a diode drop, and ifthe battery management system (BMS) opens up the charge FET, but thebattery charging device can still measure a battery voltage greater than(>) 10.5 volts, it can determine that the lithium ion rechargeablebattery is still connected, and next the battery charging device has tobe able to determine when the charge FET closes again.
 31. The methodaccording to claim 39, wherein to determine when the charge FET closesagain, the lithium ion rechargeable battery impedance is repeatedlypolled.
 32. The method according to claim 31, wherein the lithium ionrechargeable battery impedance is polled every minute.
 33. The methodaccording to claim 31, wherein during the polling the lithium ionbattery impedance, the battery charging device attempts to force acharge current, and if no current is accepted, the battery chargingdevice knows that the charge FET is still open, and once the charge FETcloses, and on the next battery charging device polling attempt, thebattery charging device will see that the lithium ion rechargeablebattery is now accepting current, and will continue charging at a firstsoft start level until the battery reaches 14.6V or until the batterymanagement system (BMS) opens up the charge FET, and if 14.6V isreached, it goes into the first lithium cell balancing mode, and if thebattery management system (BMS) opens up, it repeats the second lithiumcell balancing mode.
 34. The method according to claim 33, wherein thepolling of the lithium ion rechargeable battery is conducted by thefirst lithium cell balancing mode, the second lithium cell balancingmode, or combined second lithium cell balancing mode and then the firstlithium cell balancing mode for a set time during the lithium cellbalancing operation.